Originally intended as a separate download -- or at least released that way in beta form -- Opera Unite now comes bundled with the release of Opera 10.10 beta as a standard feature.

Opera Unite is a peer-to-peer system with an API that allows developers to create feature-rich apps using only HTML, CSS, and JavaScript. Or as Opera describes it, a Web server in the Web browser. The software ships with six pre-installed apps, including photo sharing, an instant messenger, file sharing, a Web server, media player, and an app called "the fridge," which allows users to share notes with friends and family.

You can view a corny YouTube video of Unite here, which looks like it took a page from Microsoft's Launch Party video. If you want to give a whirl yourself, grab the download here.